The present disclosure is directed to a clutch assembly and, more particularly, to a noiseless one-way clutch assembly, also known as a freewheel.
Clutch assemblies have various uses. One common form of a clutch assembly is as a bicycle hub. More particularly, the hub of the drive-side wheel (usually the rear wheel) of a bicycle is sometimes provided with an integrated or separate clutch assembly referred to as a freewheel. The freewheel is usually equipped with a one-way clutch mechanism so that only unidirectional rotational force is transmitted to the bicycle wheel. One-way clutch mechanisms having various structures are known. One known example is a ratchet mechanism in which engagement between pawls and ratchet teeth is employed. When pedals drive a chain and the chain rotatably drives a cog, the ratchet mechanism transmits the torque from the ratchet teeth to the pawls and rotatably drives an inner component. The pawls are actuated by pawl springs in such a way as to ensure constant engagement with the ratchet teeth. The ratchet mechanism must possess extremely high strength and shock resistance because considerable torque and impact forces are transmitted from the ratchet teeth to the pawls.
When the pedals are stopped or rotated backward, the inner component of the freewheel rotates together with the wheel, creating a rotational movement in relation to the ratchet teeth. Because the inner component has pawls, the pawls and the ratchet teeth move relative to each other. Since the pawls are constantly actuated and pressed against the tooth surfaces of the ratchet teeth by pawl springs, the pawls chatter against the teeth surfaces of the ratchet teeth when performing a rocking movement in conformity with the peaks and valleys of the ratchet teeth. The noise generated by such a ratchet mechanism is unpleasant for the cyclist, and the friction between the pawls and the tooth surfaces of the ratchet teeth wastes energy. The result is that this type of friction wears out the pawls and the tooth surfaces of the ratchet teeth, thus shortening the life of the freewheel.
Other freewheel mechanisms have been employed, offering noiseless operation. In nearly all instances, however, added materials (and mass) have been used to control the relative position of the pawl by the provision of a separate mechanism responsive to the direction of the movement of the driving member. This adds to the complexity and cost of the freewheel. Other known clutch mechanisms that offer noiseless operation are roller or sprag clutches. In these systems, the operation is noiseless but the clutch components remain in constant contact, even when disengaged, resulting in systems that produce high friction and wear.